u2 - dna structure/replication

Question 1

bonds in nucleotides

Answer 1

1. carbon 3 of the pentose sugar attaches to the phosphate of the next nucleotide –> forms sugar phosphate backbone
2. c3 and c5 attaches to phosphates via a PHOSPHODIESTER BOND
3. c1 attaches to nitrogenous base via GLYCOSAL BOND

Question 2

purines

Answer 2

adenine, guanine
- double ringed

Question 3

pyrimidines

Answer 3

cytosine, thymine, uracil
- single ringed

Question 4

adenine and thymine

Answer 4

has 2 hydrogen bonds

Question 5

cytosine and guanine

Answer 5

has 3 hydrogen bonds

Question 6

dna structure

Answer 6

• antiparallel (are parallel but run in opposite directions)
• one runs in 5’ to 3’ direction, other runs in 3’ to 5’ direction

Question 7

bonds in dna molecule

Answer 7

hydrogen bonds, phosphodiester bonds, glycosal bond

Question 8

purpose of dna replication

Answer 8

making a copy of dna before dividing so that each daughter cell has a complete copy of genetic information

Question 9

type of replication for dna

Answer 9

semi conservative

Question 10

direction for BUILDING dna

Answer 10

5’ to 3’

Question 11

order that dna enzymes work in

Answer 11

1. dna helicase
2. topoisomerase
3. single stranded binding proteins
4. primase
5. dna polymerase III
6. dna polymerase I
7. ligase

Question 12

dna helicase

Answer 12

“unzipper”
unwinds the dna by breaking hydrogen bonds between the base pairs
- forms replication fork and replicatin bubble

Question 13

topoisomerase

Answer 13

“tension relief”
relieves tension and prevents supercoiling/tangling during replication by temporarily cutting and resealing the DNA double helix

Question 14

single stranded binding proteins (SSBs)

Answer 14

binds to unwinded dna (exposed single strands) to stabilize and to prevent it from rebonding and closing
- blocking hydrogen bonds between bases

Question 15

primase

Answer 15

“initializer”
lays down rna primers to the 3’ end of both strands for dna polymerase to have a starting point

Question 16

DNA polymerase III

Answer 16

“builder”
adds new nucleotides from the ends of the rna primers
- builds onto the 3’ end

Question 17

leading strand

Answer 17

dna strand that builds CONTINUOUSLY towards the replication fork
- only needs one rna primer

Question 18

lagging strand

Answer 18

dna strand that build DISCONTINUOUSLY away from replication fork
- need several rna primers

Question 19

dna polymerase I

Answer 19

“replacer”
removes RNA primers to replace them with correct DNA nucleotides

Question 20

dna ligase

Answer 20

“gluer”
joins gaps between okazaki fragments by making phosphodiester bonds
- also connects pieces from different replication bubbles

Question 21

exonucleases

Answer 21

removes incorrect base when proofreading dna strand

Question 22

levene

Answer 22

discovered that nucleotides are composed of a phosphate group, a pentose sugar and nitrogenous base
- dna being formed from polynucleotide chains

Question 23

franklin

Answer 23

produced the first image of DNA using x-ray crystallography to show DNA

Question 24

miescher

Answer 24

observed dna by breaking down nucleus of wbcs
- found nuclein, which was a grey substance that had new chemical properties

Question 25

chargaff

Answer 25

chargaff's rule: in dna, the total number of purines is equal to the total number of pyrimidines

Question 26

watson and crick

Answer 26

researched shape of dna, found that it was a double helix